The purpose of this research study is to learn whether panitumumab helps treat colorectal cancer in participants who have not responded to treatment with cetuximab. Panitumumab is a human monoclonal antibody. Antibodies are proteins that recognize a foreign substance in the body and then attach themselves to it making it exposed to destruction. Panitumumab attaches itself to a protein on cancer cells called "epidermal growth factor receptor" or EGFR. EGFR helps cancer cells to grow, and blocking EGFR helps prevent cancer cells from growing.